Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

An ornamental diamond is provided as an extremely bright diamond with
numerous reflection patterns when viewed from above its table facet and
crown facets. The diamond has the same crown as the round brilliant cut
and its pavilion consists of a first pavilion and a second pavilion
separated by a horizontal division plane. The second pavilion is an
octagonal pyramid and its side faces form second pavilion main facets.
The first pavilion is a hexadecagonal frustum with a top face on the
horizontal division plane and its side faces form first lower girdle
facets. First pavilion main facets extend from the girdle and between the
first lower girdle facets, into between the second pavilion main facets.
The ornamental diamond having the two-stage pavilion is much more
brilliant than and has twice as many reflection patterns as the
conventional round brilliant cut.

Claims:

1. A cut design of diamond comprising:a girdle of a round or polygonal
shape having an upper horizontal section surrounded by an upper periphery
and, a lower horizontal section surrounded by a lower periphery and being
parallel to the upper horizontal section;a crown of a substantially
polygonal frustum formed above the upper horizontal section of the girdle
and upward from the girdle, said crown having a table facet of a regular
octagon which forms a top surface of the polygonal frustum; anda pavilion
of a substantially polygonal pyramid formed below the lower horizontal
section of the girdle and downward from the girdle and having a bottom
apex,wherein, according to the following definition: a Z-axis is defined
along a straight line extending from the bottom apex of the polygonal
pyramid pavilion through a center of the table facet; first planes are
defined as planes including the Z-axis and passing eight respective
vertexes of the table facet; an X-axis is defined along a straight line
passing a point where a first plane intersects with the girdle lower
periphery, and being perpendicular to the Z-axis; a Y-axis is defined
along a straight line passing a point where a first plane perpendicular
to the Z-axis and the X-axis intersects with the girdle lower periphery,
and being perpendicular to the Z-axis and the X-axis; and second planes
are defined as planes each of which includes the Z-axis and bisects an
angle between two adjacent first planes,the crown has eight bezel facets,
eight star facets, and sixteen upper girdle facets, as well as the table
facet, each bezel facet is a quadrilateral plane whose opposite vertexes
are a vertex of the table facet and a point where a first plane passing
said vertex intersects with the girdle upper periphery, said
quadrilateral plane has the other two opposite vertexes on respective
adjacent second planes and shares a vertex out of the other two opposite
vertexes with an adjacent bezel facet, each star facet is an isosceles
triangle composed of the base of a side of the table facet and the vertex
shared by two adjacent bezel facets whose vertexes are at the two ends of
the base, and each upper girdle facet is a triangle composed of one side
intersecting at one end with the girdle upper periphery, out of the sides
of each bezel facet, and a point where a second plane passing the other
end of said side intersects with the girdle upper periphery,wherein the
pavilion comprises a first pavilion and a second pavilion separated by a
horizontal division plane parallel to the lower horizontal section of the
girdle, the first pavilion has eight first pavilion main facets and
sixteen first lower girdle facets, each first pavilion main facet is a
quadrilateral plane having a vertex at a point where a first plane
intersects with the girdle lower periphery, opposite vertexes at two
points on the horizontal division plane equidistant from the first plane,
and the other vertex on the first plane, and being perpendicular to the
first plane, each first lower girdle facet is a quadrilateral plane
located between the lower horizontal section of the girdle and the
horizontal division plane, sharing a side connecting the vertex on the
girdle lower periphery and the vertex on the horizontal division plane of
the first pavilion main facet, with the first pavilion main facet, and
located between said side and a second plane, the second pavilion has
eight second pavilion main facets, and each second pavilion main facet is
a hexagonal plane located between two adjacent first planes and
surrounded by two sides connecting the bottom apex and the other vertexes
on the first planes of two respective adjacent first pavilion main facets
intersecting with said two respective first planes, two sides connecting
the other vertexes and the vertexes on the horizontal division plane
shared with said two respective adjacent first pavilion main facets, and
two sides connecting the vertexes on the horizontal division plane of two
respective first lower girdle facets located between said two first
pavilion main facets, and a vertex on a second plane shared by the two
first lower girdle facets,wherein a first pavilion angle (p1) between the
first pavilion main facet and the lower horizontal section of the girdle
is from 40.degree. to 46.degree.,wherein in a graph with the first
pavilion angle (p1) on the horizontal axis and a crown angle (c) between
the bezel facet and the lower horizontal section of the girdle on the
vertical axis, the crown angle (c) falls within a region between two
straight lines, one connecting two points where (p1, c) is (40, 29.6) and
(43, 14.4) and the other connecting two points where (p1, c) is (43,
14.4) and (46, 14.4), and two straight lines, one connecting two points
where (p1, c) is (40, 36.3) and (43, 23.3) and the other connecting two
points where (p1, c) is (43, 23.3) and (46, 17.8),wherein in a graph with
the first pavilion angle (p1) on the horizontal axis and a second
pavilion angle (p2) between the second pavilion main facet and the lower
horizontal section of the girdle on the vertical axis, the second
pavilion angle (p2) falls within a region between two straight lines, one
connecting two points where (p1, p2) is (40, 35.7) and (44, 37.55) and
the other connecting two points where (p1, p2) is (44, 37.55) and (46,
37.3), and a straight line connecting two points where (p1, p2) is (40,
39.35) and (46, 39.35), andwherein when an X-axis coordinate of a point
where the girdle lower periphery intersects with the X-axis is 2.0, an
X-axis coordinate (del) of a vertex of the regular octagon of the table
facet present on the X-axis is from 0.9 to 1.2.

Description:

TECHNICAL FIELD

[0001]The present invention relates to a cut design of ornamental diamond
and, more particularly, to a novel cut design allowing a viewer of a
diamond to sense more beauty.

BACKGROUND ART

[0002]Diamond is cut for use in ornamentation to obtain a brilliant
diamond and accessory and there are the round brilliant cut ornamental
diamond and accessory of a 58-faceted body.

[0003]Mathematician Tolkowsky proposed a cut believed to be ideal, as a
design to enhance brilliance of the round brilliant cut ornamental
diamond, which has the pavilion angle of 40.75°, the crown angle
of 34.50°, and the table diameter of 53% of the girdle diameter. A
design developed from it is one called the GIA (Gemological Institute of
America) system.

[0004]The inventors conducted study on cuts to enhance brilliance of
ornamental diamonds and proposed in Patent Document 1, the cut design
wherein the pavilion angle p was between 45° and 37.5° both
inclusive and the crown angle (c) fell within the range of
-3.5×p+163.6≧c≧-3.8333×p+174.232, as one
permitting a viewer who views a round brilliant cut diamond from above
the table facet thereof, to simultaneously view light emerging from the
crown facets after incidence into the crown facets, light emerging from
the crown facets after incidence into the table facet, and light emerging
from the table facet after incidence into the crown facets. In the cut
design, the center value of the pavilion angle p is 38.5° and that
of the crown angle (c) is 27.92°. Since the round brilliant cut
diamonds are designed with emphasis on the brilliance of the crown facets
as well as the brilliance of the table facet, the diameter of the table
facet is from 40 to 60% of that of the girdle, and it is from 33 to 60%
in the diamond proposed before by the inventors.

[0005]The brilliance of an ornamental diamond is sensed by a viewer in
such a manner that light is incident from the outside into the diamond
and the incident light is reflected inside the diamond to reach the
viewer. The degree of brilliance of a diamond is determined by a quantity
of the reflected light from the diamond. The quantity of reflected light
is usually evaluated by a physical quantity of reflected light.

[0006]The human perception, however, is not determined by the physical
quantity of reflected light only. For letting a viewer sense beauty of a
diamond, the diamond needs to provide a large quantity of light to be
sensed by the viewer, i.e., a large quantity of physiologically or
psychologically visually-perceived reflected light. There are the
Fechner's law and Stevens' law as to the quantity of light perceived by
humans (cf. Non-patent Document 1). The Fechner's law states that the
quantity of visually-perceived light is the logarithm of the physical
quantity of light. When the Stevens' law is applied on the assumption
that a light source is a point light source, the quantity of
visually-perceived light is the square root of the physical quantity of
light. Based on either of the Fechner's and Stevens' laws, many
conclusions are considered to be substantially identical without
significant error though they are quantitatively different. Then the
inventors adopted the Stevens' law to evaluate the quantity of reflected
light from the diamond and thereby to determine the quantity of
visually-perceived light, and evaluated the brilliance of diamond, based
on the quantity of visually-perceived reflected light in the case of the
visually-perceived light being the reflected light. We proposed in Patent
Document 2 that the quantity of reflected light from the diamond, though
it must be different depending upon illumination conditions, was to be
evaluated in such a practical condition that incident light to be blocked
by the viewer and incident light coming from sufficiently far distances
were excluded from incident light from a planar light source with uniform
luminance and the quantity of effective visually-perceived reflected
light was evaluated using reflection of the remaining incident light, and
also proposed a design of brilliant cut diamond capable of increasing the
quantity of effective visually-perceived reflected light.

[0008]We studied how to further increase the quantity of effective
visually-perceived reflected light by modifying the round brilliant cut
design of diamond and accomplished the present invention. It is thus an
object of the present invention to provide an ornamental diamond having a
two-stage pavilion with numerous reflection patterns, which allows a
viewer to sense extreme brightness when the diamond is viewed from above
the table facet and crown facets thereof.

Means for Solving the Problem

[0009]An ornamental diamond having a two-stage pavilion according to the
present invention comprises: a girdle of a round or polygonal shape
having an upper horizontal section surrounded by an upper periphery and,
a lower horizontal section surrounded by a lower periphery and being
parallel to the upper horizontal section; a crown of a substantially
polygonal frustum formed above the upper horizontal section of the girdle
and upward from the girdle, the crown having a table facet of a regular
octagon which forms a top surface of the polygonal frustum; and a
pavilion of a substantially polygonal pyramid formed below the lower
horizontal section of the girdle and downward from the girdle and having
a bottom apex. The pavilion comprises a first pavilion and a second
pavilion separated by a horizontal division plane parallel to the lower
horizontal section of the girdle. It should be noted herein that there is
no face like a facet between the first pavilion and the second pavilion
and that a horizontal plane to separate the first pavilion and the second
pavilion is called the "horizontal division plane," for convenience' sake
of description in the present invention.

[0010]The crown has eight bezel facets, eight star facets, and sixteen
upper girdle facets, as well as the table facet. The first pavilion has
eight first pavilion main facets and sixteen first lower girdle facets.
The second pavilion has eight second pavilion main facets.

[0011]In the diamond of the present invention, a Z-axis is defined along a
straight line extending from the bottom apex of the polygonal pyramid
pavilion through a center of the table facet; first planes are defined as
planes including the Z-axis and passing eight respective vertexes of the
table facet; an X-axis is defined along a straight line passing a point
where a first plane intersects with the girdle lower periphery, and being
perpendicular to the Z-axis; a Y-axis is defined along a straight line
passing a point where a first plane perpendicular to the Z-axis and the
X-axis intersects with the girdle lower periphery, and being
perpendicular to the Z-axis and the X-axis; and second planes are defined
as planes each of which includes the Z-axis and bisects an angle between
two adjacent first planes.

[0012]In the crown, each bezel facet is a quadrilateral plane whose
opposite vertexes are a vertex of the table facet and a point where a
first plane passing the mentioned vertex intersects with the girdle upper
periphery, and the quadrilateral plane has the other two opposite
vertexes on respective adjacent second planes and shares a vertex out of
the other two opposite vertexes with an adjacent bezel facet. Each star
facet is an isosceles triangle composed of the base of a side of the
table facet and the vertex shared by two adjacent bezel facets whose
vertexes are at the two ends of the base. Each upper girdle facet is a
triangle composed of one side intersecting at one end with the girdle
upper periphery, out of the sides of each bezel facet, and a point where
a second plane passing the other end of the side intersects with the
girdle upper periphery.

[0013]The second pavilion is an octagonal pyramid located between the
bottom apex and the horizontal division plane and having ridge lines
passing the bottom apex, on the respective first planes, and the side
faces of the octagonal pyramid form the second pavilion main facets. The
first pavilion is a hexadecagonal frustum located between the girdle
lower periphery and the horizontal division plane and having ridge lines
on the respective first planes and on the respective second planes, and
the side faces of the hexadecagonal frustum form the first lower girdle
facets. Each first pavilion main facet is a quadrilateral plane having a
vertex at a point where a first plane intersects with the girdle lower
periphery, being perpendicular to the first plane, and having a
predetermined angle with respect to the lower horizontal section of the
girdle (which corresponds to "first pavilion angle" described below), the
quadrilateral plane has another vertex on a ridge line between two
adjacent second pavilion main facets extending in the second pavilion,
and the other two vertexes on the horizontal division plane, and these
two vertexes are equidistant from the first plane. The first pavilion
main facet extends into the second pavilion so as to cut off a part of
each side face of the octagonal pyramid of the second pavilion whereby
the second pavilion main facets are formed from the respective side faces
of the octagonal pyramid of the second pavilion, and it cuts off a part
of each side face of the hexadecagonal frustum of the first pavilion
whereby the first lower girdle facets are formed from the respective side
faces of the hexadecagonal frustum of the first pavilion. Since each
second pavilion main facet extends into the first pavilion and has one
vertex on a ridge line between two adjacent first girdle facets, the side
faces of the hexadecagonal frustum of the first pavilion are further cut
off by the second pavilion main facets to form the first lower girdle
facets.

[0014]In the first pavilion, each first pavilion main facet is a
quadrilateral plane having a vertex at a point where a first plane
intersects with the girdle lower periphery, opposite vertexes at two
points on the horizontal division plane equidistant from the first plane,
and the other vertex on the first plane, and being perpendicular to the
first plane. Each first lower girdle facet can be said to be a
quadrilateral plane located between the lower horizontal section of the
girdle and the horizontal division plane, sharing a side connecting the
vertex on the girdle lower periphery and the vertex on the horizontal
division plane of the first pavilion main facet, with the first pavilion
main facet, and located between the mentioned side and a second plane.

[0015]In the second pavilion, each second pavilion main facet can be said
to be a hexagonal plane located between two adjacent first planes and
surrounded by two sides connecting the bottom apex and the other vertexes
on the first planes of two respective adjacent first pavilion main facets
intersecting with the two respective first planes, two sides connecting
the other vertexes and the vertexes on the horizontal division plane
shared with the two respective adjacent first pavilion main facets, and
two sides connecting the vertexes on the horizontal division plane of two
respective first lower girdle facets located between the two first
pavilion main facets, and a vertex on a second plane shared by the two
first lower girdle facets.

[0016]In the ornamental diamond having the two-stage pavilion according to
the present invention, a first pavilion angle (p1) between the first
pavilion main facet and the lower horizontal section of the girdle is
from 40° to 46°; in a graph with the first pavilion angle
(p1) on the horizontal axis and a crown angle (c) between the bezel facet
and the lower horizontal section of the girdle on the vertical axis, the
crown angle (c) falls within a region between two straight lines, one
connecting two points where (p1, c) is (40, 29.6) and (43, 14.4) and the
other connecting two points where (p1, c) is (43, 14.4) and (46, 14.4),
and two straight lines, one connecting two points where (p1, c) is (40,
36.3) and (43, 23.3) and the other connecting two points where (p1, c) is
(43, 23.3) and (46, 17.8); in a graph with the first pavilion angle (p1)
on the horizontal axis and a second pavilion angle (p2) between the
second pavilion main facet and the lower horizontal section of the girdle
on the vertical axis, the second pavilion angle (p2) falls within a
region between two straight lines, one connecting two points where (p1,
p2) is (40, 35.7) and (44, 37.55) and the other connecting two points
where (p1, p2) is (44, 37.55) and (46, 37.3), and a straight line
connecting two points where (p1, p2) is (40, 39.35) and (46, 39.35).

[0017]When an X-axis coordinate of a point where the girdle lower
periphery intersects with the X-axis is 2.0, an X-axis coordinate (del)
of a vertex of the regular octagon of the table facet present on the
X-axis is from 0.9 to 1.2.

EFFECT OF THE INVENTION

[0018]A reflection rating index of the ornamental diamond with the
two-stage pavilion of the present invention is far greater than that of
the excellent-grade round brilliant cut diamond, 400.

[0019]The number of reflection patterns of the ornamental diamond with the
two-stage pavilion of the present invention is nearly double that of the
excellent-grade round brilliant cut diamond, 67, and larger than that of
the round brilliant cut diamond proposed before by the inventors, 85.

[0020]As described above, the ornamental diamond with the two-stage
pavilion of the present invention shows the greater brilliance of
reflection and the larger number of reflection patterns than the
conventional ones and is thus excellent for ornamental use.

BRIEF DESCRIPTION OF DRAWINGS

[0021]FIG. 1 is a plan view of an ornamental diamond having a two-stage
pavilion according to the present invention.

[0022]FIG. 2 is a side view of the ornamental diamond having the two-stage
pavilion according to the present invention.

[0023]FIG. 3 is a bottom view of the ornamental diamond having the
two-stage pavilion according to the present invention.

[0024]FIG. 4 is an explanatory sectional view in the ZX plane of the
ornamental diamond with the two-stage pavilion shown in FIGS. 1, 2, and
3.

[0025]FIG. 5 is an explanatory sectional view in a second plane of the
ornamental diamond with the two-stage pavilion shown in FIGS. 1, 2, and
3.

[0026]FIG. 6 is a graph of first pavilion angle on the horizontal axis
versus crown angle on the vertical axis to show a region of the crown
angle and first pavilion angle in the ornamental diamond with the
two-stage pavilion according to the present invention.

[0027]FIG. 7 is a graph of first pavilion angle on the horizontal axis
versus second pavilion angle on the vertical axis to show a region of the
second pavilion angle and first pavilion angle in the ornamental diamond
with the two-stage pavilion according to the present invention.

[0028]FIG. 8 is a graph showing a relation of reflection rating index and
crown angle of ornamental diamonds with the two-stage pavilion according
to the present invention, using the first pavilion angle as a parameter.

[0029]FIG. 9 is a graph showing a relation of reflection rating index and
second pavilion angle of ornamental diamonds with the two-stage pavilion
according to the present invention, using the first pavilion angle as a
parameter.

[0030]FIG. 10 is a drawing showing reflection patterns of the ornamental
diamond with the two-stage pavilion according to the present invention.

[0053]FIGS. 1 to 3 are drawings to show the appearance of a diamond 100
having a two-stage pavilion according to the present invention and FIGS.
4 and 5 are explanatory sectional views thereof, wherein FIG. 1 is a plan
view, FIG. 2 a side view, and FIG. 3 a bottom view. The top surface of
the diamond 100 herein is a table facet 112 of a regular octagon, and a
girdle 120 is of a round or polygonal shape and is located between an
upper horizontal section 124 surrounded by a girdle upper periphery 122
and, a lower horizontal section 128 surrounded by a girdle lower
periphery 126 and being parallel to the upper horizontal section 124.
There is a crown 110 of a substantially polygonal frustum formed above
the girdle upper horizontal section 124 and upward from the girdle 120,
and the table facet 112 of the regular octagon forms the top surface of
the polygonal frustum. There is a pavilion 130 of a substantially
octagonal pyramid formed below the girdle lower horizontal section 128
and downward from the girdle 120 and there is a portion called a culet at
a center bottom apex G thereof. In the periphery of the crown 110 there
are usually eight bezel facets 114, eight star facets 116 formed between
the periphery of the table and the bezel facets 114, and sixteen upper
girdle facets 118 formed between the girdle 120 and the bezel facets 114.
The pavilion 130 has a horizontal division plane 134 parallel to the
girdle lower horizontal section 128, approximately at the middle of the
height thereof and it separates the pavilion 130 into a first pavilion
132 above the horizontal division plane 134 and a second pavilion 142
below the horizontal division plane 134. In the periphery of the first
pavilion 132 there are eight first pavilion main facets 136 formed, and
totally sixteen first lower girdle facets 138, two formed between each
pair of two first pavilion main facets 136. The outer surface of the
girdle 120 is perpendicular to the table facet 112. The second pavilion
142 has eight second pavilion main facets 146 in the periphery thereof.

[0054]Let us define a Z-axis along a straight line extending from the
bottom apex G of the octagonal pyramid pavilion 130 through the center of
the table facet, first planes 102 as planes including the Z-axis and
passing the respective vertexes of the octagon of the table facet, and
second planes 104 as planes each passing the Z-axis and bisecting an
angle between two adjacent first planes 102.

[0055]For convenience' sake of description, as shown in FIGS. 1 to 5,
orthogonal coordinate axes (right-hand system) are set in the diamond 100
and the Z-axis thereof is made coincident with the aforementioned
straight line (Z-axis) extending from the bottom apex G of the octagonal
pyramid pavilion through the center of the table facet. The X-axis is
defined along a straight line passing a point where a first plane 102
intersects with the girdle lower periphery 126, and being perpendicular
to the Z-axis, and the Y-axis is defined along a straight line
perpendicular to the Z-axis and the X-axis. The origin O of the X-axis,
Y-axis, and Z-axis is located at the center of the girdle lower
horizontal section 128. The diamond 100 has eightfold symmetry around the
Z-axis and the Z-axis is perpendicular to the table facet 112, the girdle
upper horizontal section 124, the girdle lower horizontal section 128,
and the pavilion horizontal division plane 134. In FIG. 4 the Y-axis is
not depicted because it is directed from the origin O into the far side
of the drawing.

[0056]The first planes are the ZX plane, the YZ plane, and planes obtained
by rotating those planes by 45° around the Z-axis, and are denoted
by 102 in FIGS. 1 and 3. The second planes are planes obtained by
rotating the first planes 102 by 22.5° around the Z-axis and are
denoted by 104 in FIGS. 1 and 3.

[0057]With reference to FIG. 1, each bezel facet 114 is a quadrilateral
plane having opposite vertexes at one vertex (e.g., A in FIG. 1) of the
regular octagon table facet 112 and at a point B where the first plane
102 passing the vertex A (e.g., the ZX plane) intersects with the girdle
upper periphery 122, and the quadrilateral plane has the other two
opposite vertexes C and D on respective second planes 104 adjacent
thereto and shares the vertex C or D with an adjacent bezel facet 114.
Each star facet 116 is a triangle AA'C composed of one side AA' of the
regular octagon table facet 112 and a vertex C shared by two bezel facets
114 a vertex of each of which is at either of the two ends A and A' of
the foregoing side. Each upper girdle facet 118 is a plane composed of
one side (e.g., CB) intersecting with the girdle upper periphery 122, out
of the sides of each bezel facet 114, and a point E where the second
plane 104 passing the other end C of the foregoing side intersects with
the girdle upper periphery 122.

[0058]With reference to FIGS. 2 and 3, each first pavilion main facet 136
of the first pavilion 132 is a quadrilateral plane FKHK' having a vertex
at a point F where a first plane 102 (e.g., the ZX plane) intersects with
the girdle lower periphery 126, the opposite vertexes at two points K and
K' on the horizontal division plane which are equidistant from the first
plane 102, and the other vertex H on the first plane, and being
perpendicular to the first plane. Each first lower girdle facet 138 is a
quadrilateral plane FJLK surrounded by a portion FJ of the girdle lower
periphery 126 between a first plane 102 and a second plane 104 adjacent
to each other, a side FK of the first pavilion main facet 136 having the
vertex F on the first plane 102, and a side JL on the second plane 104
passing a point J where the second plane 104 intersects with the girdle
lower periphery 126, and shared with an adjacent first lower girdle
facet. The first pavilion 132 is a portion of the pavilion 130 located
between the girdle lower section 128 and the horizontal division plane
134 and each first pavilion main facet 136 projects through the
horizontal division plane 134 toward the bottom apex G The first pavilion
132 has the peripheral surface composed of eight first pavilion main
facets 136 and sixteen first lower girdle facets 138. When the projecting
portions of the first pavilion main facets 136 from the horizontal
division plane 134 toward the bottom apex G are excluded, the first
pavilion 132 can be regarded as a hexadecagonal frustum having a top face
on the horizontal division plane 134 and a bottom face on the girdle
lower section 138, each side face of the hexadecagonal frustum
corresponds to a first lower girdle facet 138, and the first lower girdle
facets 138 are made by removing parts of the respective side faces by the
first pavilion main facets 136 and the extending portions of the second
pavilion main facets 146.

[0059]In the second pavilion 142, each second pavilion main facet 146 is a
hexagonal plane GHKLK''H' having a vertex at the pavilion bottom apex G
and surrounded by two sides GH and GH' on two adjacent first planes 102,
side HK and side H'K'' of two adjacent first pavilion main facets 136,
and side KL and side K''L connecting vertexes K and K'' of two respective
first lower girdle facets 138 on the horizontal division plane 134
between two adjacent first pavilion main facets 136, and a vertex L on
the second plane shared by the two first lower girdle facets 138. The
second pavilion 142 is a portion of the pavilion 130 between the
horizontal division plane 134 and the pavilion bottom apex G, but each
second pavilion main facet 146 projects through the horizontal division
plane 134 toward the girdle 120. The second pavilion 142 has the
peripheral surface composed of eight second pavilion main facets 146.
When the projecting portions of the first pavilion main facets 136
through the horizontal division plane 134 toward the bottom apex G and
the projecting portions of the second pavilion main facets 146 through
the horizontal division plane 134 toward the girdle 120 are excluded, the
second pavilion 142 can be regarded as an octagonal pyramid having an
apex at the bottom apex G and a bottom surface on the horizontal division
plane 134, each side face of the octagonal pyramid corresponds to a
second pavilion main facet 146, and the second pavilion main facets 146
are made by removing parts of the respective side faces by the first
pavilion main facets 136.

[0060]Each of the bezel facets 114 and each of the first pavilion main
facets 136 are located between two adjacent second planes 104. Each first
pavilion main facet 136 is located between two adjacent second planes 104
and is perpendicular to a first plane 102. The common side CE of two
adjacent upper girdle facets 118, and the common side LJ of two adjacent
first lower girdle facets 138 are on a second plane 104. Each star facet
116, two upper girdle facets 118 sharing the side CE, and two first lower
girdle facets 138 sharing the side LJ are located between two adjacent
first planes 102. These two upper girdle facets 118 and these two first
lower girdle facets 138 are located at positions approximately opposite
to each other with the girdle 120 in between.

[0061]Each of the first planes 102 divides the center of each bezel facet
114 and the center of each first pavilion main facet 136. For this
reason, each bezel facet 114 is approximately opposed to each first
pavilion main facet 136 with the girdle 120 in between.

[0062]In the description hereinafter, the size of each part of the diamond
will be expressed based on the radius of the girdle as a reference.
Namely, each part is expressed by its X-axis coordinate based on the
definition that the X-axis coordinate of a point where the girdle lower
periphery 126 intersects with the X-axis is defined as 2.0. The girdle
height (h) is a length in the Z-axis direction of the girdle 120 and is
expressed by a value based on the girdle radius of 2.0.

[0063]In the sectional view in the ZX plane shown in FIG. 4 and the
sectional view in the second plane 104 shown in FIG. 5, the same portions
as those in FIGS. 1 to 3 are denoted by the same reference symbols. An
angle between the bezel facet 114 of the crown 110 and the girdle lower
horizontal section 128 (XY plane), i.e., crown angle is represented by c
and an angle between the first pavilion main facet 136 of the first
pavilion 132 and the girdle lower horizontal section 128 (XY plane),
i.e., first pavilion angle by p1. An angle between the second pavilion
main facet 146 of the second pavilion 142 and the girdle lower horizontal
section 128 (XY plane), i.e., second pavilion angle is represented by p2.
In the present specification, the bezel facets, star facets, and upper
girdle facets in the crown are sometimes called the crown facets
together, and the first and second pavilion main facets and the first
lower girdle facets in the pavilion the pavilion facets together.

[0064]The girdle height (h), table radius (del), distance to the tip of
the star facet (fx), distance to the lower vertex of the first pavilion
main facet extending into the second pavilion (Gd), and position of the
horizontal division plane of the pavilion (ax) are indicated by their
respective X-axis coordinates, as shown in FIGS. 1, 3, 4, and 5. The
table radius (del) is the X-axis coordinate of the vertex A of the
regular octagon of the table facet 112 on the X-axis as shown in FIG. 1,
and is preferably within the range of 0.9 to 1.2. If the table radius is
smaller than 0.9, light reflected in the first pavilion will become less
likely to directly reach the table facet, so as to darken the table
facet. If the table radius is larger than 1.2 on the other hand, the
crown facets will become dark. If the table radius is off the range of
0.9 to 1.2, the number of reflection patterns will become smaller. The
table radius (del) is thus preferably from 0.9 to 1.2. The distance to
the tip of the star facet (fx) is the X-axis coordinate of the vertex C
(or D) which the bezel facet 114 intersecting with the first plane
including the X-axis shares with the adjacent bezel facet 114, and is a
projection on the ZX plane of a distance from the Z-axis to the tip of
the star facet. The distance to the lower vertex of the first pavilion
main facet extending into the second pavilion 142 (Gd) is the X-axis
coordinate of the vertex H on the pavilion bottom apex G side of the
first pavilion main facet 136. An X-axis coordinate (ax) of an
intersecting point between the periphery of the horizontal division plane
and the first plane including the X-axis is used for expressing the place
of the horizontal division plane 134 which separates the pavilion 130
into the first pavilion 132 and the second pavilion 142.

[0065]For defining the dimensions (size) of the diamond, the crown height,
pavilion depth, and total depth are sometimes used in addition to the
table radius, pavilion angle, and crown angle, but these are not adopted
in the present specification because they are uniquely determined once
the table radius, first pavilion angle (p1), second pavilion angle (p2),
and crown angle (c) are given.

[0066]Introduction of Reflection Rating Index

[0067]In the study below, the diamond is set so that the Z-axis of the
diamond becomes vertical, and the diamond is observed from above the
Z-axis while being illuminated with light from light sources uniformly
distributed over a horizontal ceiling. Light incident at angles of less
than 20° relative to the Z-axis into the table facet and crown
facets of the diamond is highly likely to be blocked by a viewer. Light
incident at angles of more than 45° relative to the Z-axis has low
illuminance because of attenuation by distance and is highly likely to be
blocked by obstacles; therefore, it has little contribution to
reflection. Therefore, the light quantity of reflection patterns shall be
determined with consideration to contribution rates according to angles
of incidence of incident light relative to the Z-axis.

[0068]The visual perception of human is to sense the intensity of a small
light spot as an amount of stimulus. Therefore, the quantity of light of
reflection patterns physically obtained also needs to be converted into
an amount of visual perception sensed as a stimulus. According to the
Stevens' law, the amount of visual perception as the intensity of
stimulus sensed by a man in the case of a small light spot is
proportional to the square root of the physical quantity of light.

[0069]By applying this law, a reflection rating index is introduced as an
index obtained by using an aesthetically-perceivable minimum physical
reflection quantity as a unit, calculating a square root of a quantity of
light per reflection pattern represented as a multiple of the unit, and
taking the sum thereof. For determining the physical reflection quantity,
the radius of the diamond is cut into 200 equal meshes, a quantity of
reflected light taking account of the contribution rates is determined
for each mesh, and the sum of quantities for an identical pattern is
defined as a physical quantity of reflected light in that pattern. Since
a diamond has the radius of about several mm, each mesh has several
hundred μm2. The amount of visual perception was calculated for
only patterns having the area of not less than 100 meshes with
consideration to the level of human discrimination, and the sum thereof
was defined as the reflection rating index.

[0070]Namely, the reflection rating index=E{(physical quantity of
reflected light with consideration to contribution rates per pattern of
not less than 100 meshes)/unit of quantity of perceivable minimum
physical reflection}1/2. In this equation Σ is the summation
for reflection patterns.

[0071]Reflection Rating Index

[0072]The ornamental diamonds having the two-stage pavilion according to
the present invention were prepared with the girdle radius: 2.0 and the
table radius (radius to a vertex of the octagon) (del): 1.0, with the
first pavilion angle (p1) of 40°, 41°, 42°,
43°, 44°, 45° or 46°, and with the crown
angle (c) varying from 14° to 37°, and the reflection
rating index was determined for each of the diamonds; FIG. 8 shows a
graph of a relation of reflection rating index versus crown angle (c),
using the first pavilion angle (p1) as a parameter. As apparent from FIG.
8, the crown angle range where the reflection rating index exceeds 430
with the first pavilion angle (p1): 40° is from 29.6 to
36.3°; the crown angle range where the reflection rating index
exceeds 430 with the first pavilion angle (p1): 41° is from 24.4
to 34°; the crown angle range where the reflection rating index
exceeds 430 with the first pavilion angle (p1): 42° is from 17 to
28.6°; the crown angle range where the reflection rating index
exceeds 430 with the first pavilion angle (p1): 43° is from 14.4
to 23.3°; the crown angle range where the reflection rating index
exceeds 430 with the first pavilion angle (p1): 44° is from 14.2
to 22.3°; the crown angle range where the reflection rating index
exceeds 430 with the first pavilion angle (p1): 45° is from 14.2
to 20.8°; the crown angle range where the reflection rating index
exceeds 430 with the first pavilion angle (p1): 46° is from 14.4
to 17.8°. FIG. 6 is a graph showing the ranges of the crown angle
(c) where the reflection rating index exceeds 430, against the first
pavilion angle (p1). It is seen that the region of the first pavilion
angle (p1) and the crown angle (c) is so determined that the first
pavilion angle (p1) is in the range of 40 to 47° and that it is
between two straight lines, one connecting points where coordinates of
(p1, c) are (40, 29.6) and (43, 14.4) and the other connecting points
where (p1, c) are (43, 14.4) and (46, 14.4), and two straight lines, one
connecting points where (p1, c) are (40, 36.3) and (43, 23.3) and the
other connecting points where (p1, c) are (43, 23.3) and (46, 17.8) on
the graph shown in FIG. 6. As shown in FIG. 6, it is seen that the
preferred range of the crown angle where the reflection rating index
exceeds 430 varies depending upon values of the first pavilion angle.

[0073]Next, the ornamental diamonds having the two-stage pavilion
according to the present invention were prepared with the girdle radius:
2.0 and the table radius (del): 1.0, with the first pavilion angle (p1)
of 40°, 41°, 42°, 43°, 44°, 45°
or 46°, and with the second pavilion angle (p2) varying from
35° to 40°, and the reflection rating index was determined
for each of them; FIG. 9 shows a graph of a relation of reflection rating
index against second pavilion angle (p2), using the first pavilion angle
(p1) as a parameter. As apparent from FIG. 9, the range of the second
pavilion angle where the reflection rating index exceeds 430 with the
first pavilion angle (p1): 40° is from 35.7 to 39.35°; the
range of the second pavilion angle where the reflection rating index
exceeds 430 with the first pavilion angle (p1): 41° is from 36 to
39.8°; the range of the second pavilion angle where the reflection
rating index exceeds 430 with the first pavilion angle (p1): 42°
is from 36.2 to 39.4°; the range of the second pavilion angle
where the reflection rating index exceeds 430 with the first pavilion
angle (p1): 43° is from 36.65 to 39.85°; the range of the
second pavilion angle where the reflection rating index exceeds 430 with
the first pavilion angle (p1): 44° is from 37.55 to 39.8°;
the range of the second pavilion angle where the reflection rating index
exceeds 430 with the first pavilion angle (p1): 45° is from 37.45
to 39.6°; the range of the second pavilion angle where the
reflection rating index exceeds 430 with the first pavilion angle (p1):
46° is from 37.3 to 39.35°. FIG. 7 is a graph showing the
ranges of the second pavilion angle (p2) where the reflection rating
index exceeds 430, against the first pavilion angle (p1). It is seen that
the region of the first pavilion angle (p1) and the second pavilion angle
(p2) is so determined that the first pavilion angle (p1) is from 40 to
46° and that it is located above two straight lines, one
connecting points where coordinates of (p1, p2) are (40, 35.7) and (44,
37.55) and the other connecting points where (p1, p2) are (44, 37.55) and
(46, 37.3), and below a straight line connecting points where (p1, p2)
are (40, 39.35) and (46, 39.35) on the graph shown in FIG. 7.

[0074]When the conventional excellent-grade round brilliant cut diamond
has the pavilion angle: 41.4°, the crown angle: 32.8°, the
girdle radius: 2.0, the table radius (del): 1.14, the star facet tip
distance (fx): 1.454, the lower girdle facet lower tip distance (Gd):
0.4, and the girdle height (h): 0.12, the reflection rating index thereof
obtained is 370 and no excellent-grade round brilliant cut diamond has
the maximum index over 400. As shown in FIGS. 8 and 9, the ornamental
diamonds having the two-stage pavilion according to the present invention
have the reflection rating index over 430 in the range of the first
pavilion angle of 40 to 46°. In FIGS. 8 and 9, the solid line
represents the reflection rating index level: 400 of the conventional
example and the dashed line does the lower limit of the reflection rating
index in the present invention which is 430 higher than the conventional
level, with some margin for various conditions. For achieving the
reflection rating index higher than 430 by an appropriate combination of
the first pavilion angle, the second pavilion angle, and the crown angle,
it is necessary to set the second pavilion angle and the crown angle to
values within the regions shown in FIGS. 6 and 7, in the range of the
first pavilion angle of 40 to 46°.

[0075]Number of Reflection Patterns

[0076]FIG. 10 shows a drawing in which reflection patterns with the area
of not less than 100 meshes are depicted on the table facet and crown
facets between the X-axis and the Y-axis, in the case where the
ornamental diamond having the two-stage pavilion according to the present
invention has the first pavilion angle: 43°, the second pavilion
angle: 39°, the crown angle: 20°, the girdle radius: 2.0,
and the table radius (del): 1.0. The number of reflection patterns was
117. FIG. 11 shows a drawing in which reflection patterns with the area
of not less than 100 meshes are depicted on the table facet and crown
facets between the X-axis and the Y-axis, in the case of the conventional
excellent-grade round brilliant cut diamond described above. The number
of reflection patterns was 67. FIG. 12 shows a drawing in which
reflection patterns with the area of the not less than 100 meshes are
depicted on the table facet and crown facets between the X-axis and the
Y-axis, in the case where the round brilliant cut diamond proposed in
Patent Document 1 by the inventors has the parameters described above.
The number of reflection patterns was 85.

INDUSTRIAL APPLICABILITY

[0077]The ornamental diamond having the two-stage pavilion according to
the present invention has the number of reflection patterns approximately
twice that in the case of the conventional excellent-grade round
brilliant cut diamond and 1.2 times that of the brilliant cut proposed
before by the inventors. For this reason, the ornamental diamond having
the two-stage pavilion according to the present invention is applicable
to ornamental use.